Accuracy and efficiency are fundamental requirements of automated laboratory analytical instruments. The requirement for a high degree of accuracy follows from the importance of the executed tests in patient diagnosis and treatment. The requirement for efficiency follows from the importance of timely results in patient care. In addition, a single, high-throughput instrument may obviate the need for multiple lower-efficiency instruments, thus leading to the potential for lower capital costs.
Modern automated analytical instruments often employ racks having one or two-dimensional arrays of vial-receiving positions for enabling the presentation of patient sample-bearing vials to the instrument. Optically readable codes, such as bar codes, are typically employed on both the racks and the individual vials. For instance, one code may be disposed upon a rack for uniquely identifying the rack to the instrument. Another code may be disposed on an outer surface of each patient sample vial to provide data such as patient identity, sample characterization, assays to be performed, etc. Yet another code may be provided adjacent or otherwise in association with each vial-receiving position on a rack to enable the creation of a logical association between the patient sample vial installed therein and its specific position on the respective rack.
To facilitate the reading of the vial-specific codes, each rack position is typically provided with a slot or other aperture through which the vial code may be viewed by the code reading device, which in the case of bar codes is a bar code scanner. Operators must ensure that each vial is oriented in the respective rack position such that the code located on the vial is viewable by the code reading device. Another alternative includes the provision of codes on labels spanning a majority of the circumference of each vial. Yet another option includes the use of vials having a physical feature that requires the vial to be properly oriented upon installation into the respective rack position.
Each of these options has a deficiency. If an operator does not properly orient a vial to present a code through a viewable aperture, the instrument may not recognize the presence of the vial, thus delaying performance of necessary assays until the positioning error is detected by the operator. The use of a custom coded label raises costs and presents the possibility of inconsistency in code formats. Finally, the requirement of unique physical features on vials raises costs and obviates the use of laboratory standard vials.
Another approach to enabling an analytical instrument to confirm the presence of a vial in a rack position has been to print a code on a back wall of each position. Once a vial has been inserted in the position, the vial, its label, and its contents are intended to obscure the code. If the code reader cannot detect the back wall code for that position, the instrument assumes a vial is present. However, operator misalignment of the vial label may provide the opportunity for the code reader to detect the code, particularly if the vial and patient sample are transparent.
What is required is a means by which an analytical instrument can positively detect the presence of a vial in a rack position even if the vial coded label is improperly oriented with respect to the code reader.